Production of strip stock from polyhexamethylene adipamide



May 19, 1953 L. 1.. STOTT ET AL PRODUCTION OF STRIP STOCK FROM POLYHEXAMETHYLENE ADIPAMIDE 4 Shee.ts-$neet 1 Filed Aug. 9, 1949 7 "Ff m M. A w an I v mm I I! ll ill 1%; 1/ o 1 b \m\ $3 N 1| Q Q@ Q@ m 1 i I R. u 1 nu l l N I i u I Q mmwnmu W a a w 3 m kfl h.\ M NM QM Q at N Y N lNVENTOR 14 ATTORNEYS L. L. STOTT ETAL PRODUCTION OF STRIP STOCK FROM May 19, 1953 POLYHEXAMETHYLENE ADIPAMIDE 4 Sheets-Sheet 2 Filed Aug. 9, 1949 l VE T R fir/12% A a-M ATTORNEYS y 9, 1953 STOTT ET Al. 2,638,631

PRODUCTION OF STRIP STOCK FROM POLYHEXAMETHYLENE ADIPAMIDE Filed Aug. 9, 1949 4 sheds-sheet s ATTORNE y 9, .953 1.. L. s'ro'r'r ET-AL 2,638,631

PRODUCTION OF STRIP STOCK FROM POLYHEXAMETHYLENE ADIPAMIDE 4 Sheets-Sheet 4 Filed Aug. 9, 1949 z I V NTOR $5 A I -%m ATTORNEXS Patented May 19, 1953 PRODUCTION OF STRIP STOCK FROM POLYHEXAMETHYLENE AD'IPAMIDE Louis L. Stott and Paul L. Shurr, Reading, Pa.,

assignors to The Polymer Corporation, Reading, Pa., a corporation of Pennsylvania Application August 9, 1949, Serial No. 109,336

ing strip stock from one of the high melting nylons, i. e., from polyhexamethylene adipamide. The invention is concerned with that type of strip forming operation in which-the molten nylon is'continuously fed to the entrance nipof a pair of forming rolls, the formed strip beingdrawn from the rollsunder tension. Inthis general typeiof operation certain special problems are encountered, particularly when forming relative ly thin strip stock, for example strip stock less than .020 inch, inthickness.

The invention relates .to the establishment of certain operating temperatures for the molten nylon being fed to the rolls, and also to the drawing of the formedstripfrom the forming rolls under substantial tensionin a direction in alignment with the plane'of the pass between the rolls, such temperatures and drawing being correlated and arranged to enable production of sound strip stock even of quite thin gauge,.for instance .008 inch in thickness. v

Other objects of the invention include arrangement of the equipment to facilitate adjustment or regulation thereof so as to. accommodate the equipment to the production ofstrip' stock of different widths and thicknesses.

g It is of importancein an operation of the character referredto above that'theroll temperature be quite accurately maintained for a given condition. of strip'production; for instance with a given temperature and rate of feed of the molten nylon to the forming rolls, and with this in mind, the invention provides for accurate'maintenance of rolltemperature, by the circulation of a heat transfer medium through the rolls, as will further appear. e

A further advantage of the capability of accurate regulation of roll temperature isthat some of the properties of the formedstrip ma thereby be varied and accurately controlled at will.-' For instance, the tensile strength, elongation and rigidity may be controlled by regulation of the roll temperature.

Still other objects of the invention include provision for handling the polyamide in such manner as to minimize opportunity of the polyamide to oxidize in the molten condition, and to minimize tendency toward development of gas bubbles in the formed strip or development of surface markings thereon. a

How the foregoing and other objects and advantages are attained will appear more fully from the following description referring to the accompanying drawings, in which-' Figure 1 is a longitudinal vertical sectional view through equipment arranged for carrying out the present invention:

Figure 2 is a transverse verticalsection taken as indicated by the section line 2-2 on Figure 1;

Figure 3 isa horizontal view of certain portions of the equipment taken substantially as indicated by theline 33 on Figure 1, but with upper portions of the equipment removed;

Figure 4, is g a longitudinal sectional view through the'nozzle for delivering molten nylon to the forming rolls, the arrangement of this figure being shown on an enlarged scale;

Figure 5 is an enlarged detailed view of a portion of the nozzle shown in Figure 4;

Figure 6 is an axial sectional view through one of the forming rolls, this view being taken as indicated by the section line 6-4; on Figure 1, but being shown on an enlarged scale and also further showing connections for the circulation of a heat transfer medium through the roll;

, Figure 7i s'a plan view of the pair of forming rolls and of the connections for supplying a heat transfer medium thereto; and f I ..,Figur'e 8 is a' sectional view of a detail taken as indicated by the line 8 8 on Figure 6.

. The equipment illustrated in Figures 1 to 3, inclusive; comprises a vessel 1 adapted to contain a liquid cooling bath, the level of which appears at Lin Figure 1. Liquid may be introduced into the vessel 1 through the inlet connection 8, which the vessel 1 and serves as a support for the pair of forming rolls l ll2 which are fixed on shafts ,I,3.l4.. The mounting of the rolls themselves,

as illustrated herein conforms with that more fully disclosed and claimed in copending application of Robert C. Rahm, Serial No. 39,954, filed July 21, 1948, issued as U. S. Patent No. 2,627,085 on February 3, 1953, which application. is assigned to the assignee of the present application. The adjustment and drive mechanism associated with the rolls also conforms with the disclosure of said copending application and since the present inventionis not concerned with the arrangement of the'se parts per se, they need not be described in detail herein. Briefly, however, it is noted that the rolls are adapted to be driven from a power shaft 15 carrying gears l6ll which .mesh with gears I8-l9 fixed on shafts ,20-21, thelattershafts carrying worms, such as indicated at 22 and 23 which mesh with worm wheels such as shown in Figure 3 at 24 and 25,

. these worm wheels beingv fixed to the roll mount- 3 ing shafts I3 and I4. The roll H is adjustable with relation to the roll 12, so as to vary the spacing between the rolls by means of an adjustable support for shaft I3 including traveling blocks 26 associated with manually adjustable screws 21.

According tothe invention, a screw'extruder'is preferably employed for melting the polyamide being used and for feeding the molten polyamide. to the entrance nip of the forming rolls. The details of construction of the extruder d'evice'itself. need not be considered herein but it-maybenotedl that this device has a hopper 30 adapted to receive the polyamide in granular form; Thepolyamide is fed from this hopper into. the. bore of? the extruder proper indicated at 3|, in which a screw advances the material (toward the left when viewed as in Figure l). The material. is

heated and melted by heater elements indicated in outline at 32 and is delivered in molten condition through the nozzle 33 which has its delivery opening close to the entrance nip between the rolls lll2.

The formed strip is'delivere d' downwardly substantially vertically from the rolls in a runsuch as shown at S; This initial run of the strip'from the forming roll's is defined by placement of a guide element, preferably'a flanged roll 3-4 below the forming rolls HI'2i A'fter passage around the guide element 34, the strip travels in a run S upwardly at an incline, being drawn by the pairs of drawing rolls 35- and 36. After delivery from rolls 36, the strip material may be delivered to a trimmeror it may be wound up or otherwise packaged for shipment or the like.

The guide element 34' ism'ounted' between the lower ends of a pair of generally upright supporting. straps 3l3"l, the upper ends of these straps having slots 38 therein cooperating with supporting bolts 39 by means of which the; straps are car'- ried by supports 40 secured to the frame I. The bolts 39 serve to adjustably fix the guide element 34 in any of a variety of positions including that shown in full lines in Figure I and also otherpositions, for instance as shown in dot-and-d'ash lines at 34a in Figure 1.

For purposes which will appear more fully hereinafter, a heating or cooling coil 41 may be positioned below the surface of the liquid inthe cooling bath. This cell or. other suitable means may be employed for temperature regulation, advantageously for cooling the liquid. of the bath through which the strip is drawn after it is formed by the forming rolls.

It is preferred to employ a nozzle for the extruder of the. type shown in Figures. 4 and 5. The nozzle member 42 of this arrangement extends beyond the feeding screw of the screw extruder andis provided with a cavity 43' at its entrance end for receiving a screen pack for screening the molten nylon before entrance intothe nozzle. The nozzle member 42 is surrounded by heater elements diagrammatically indicated at 44, and the delivery nozzle proper is associated with the delivery end .of the member 42. This delivery nozzle comprises a pair of plates 45 and 4-6, the former comprising. a flat plate and the latter having an aperture 41' for cooperation with the nozzle member 42 and further having a flaring delivery recess 48 As is shown, this recess flares so as to spread the molten nylon along. the entrance nip between the rolls. In addition, the recess 48 is tapered transversely of the member 46 so that the delivery passage becomes progressively thinner as it widens toward the delivery port. This configuration is of importance since it maintains the column of material being fed under pressure all the way to the point of discharge. This aids in minimizing formation of gas bubbles in the material. Indeed, in the. construction, of the entire nozzle, the several; passages thereof- 1 are of'projgressively dimensioned cross-sectional flow area, so that somewhat of a back pressure is imposed on the material all the way back to the feeding screw in thezextmdenitselfi- Thereby the formation of gas on air bubbleswithin the material delivered from the extruden is. greatly diminished.

It. ofiinportance that the nozzle member 42 ismaintainedatatemperature above the freezing point of the polyamide and attention is also called to thewfact that the heater diagrammatically. indicated at 44 in Figure 4 extends all the way out to a point adjacent the nozzle tip, and this aids in maintaining even the nozzle tip at the desired; high temperature:

The" structure and arrangement of the forming rolls themselves is best" illustrated in Figures 6; '7- and 8. As seen in- Figure" 6; roll H- is provided with a hollow interior, being closed. atone end by the closure member 491 At its other end the shaft I3 is: alsoprovided with an interior passage through which a tube 50 projects, with its inner end lyinginternally of" the roll itself. Spaced discs: 51- are arrangcd withi n theroll; ear-h having an oversized central aperture accommodating the tube 50 and-further'having additional apertures as indicatedat52 for circulation of a heat transfer medium; Toward its-left. end when viewed" as in Figure S, the tube 50-i's extended for connection with theflexible hose orthe like 53. Another flexible hose 54' communicates with the annular passage 55 formed between the tube 50 and" the inner wall of rollshaft I 32 this-latter connection being made tl-ircugh a fitting 56.- Suitable internal rotative joints are provided to ac.- commodate rotation. of the roll- H- and its shaft [3, independently of the fluid supply and discharge. connections 53,. 54 and 56-. Circulationof heat transfer medium is effected by introducing such medium through the flexible hose 53 from which. it.- is delivered to the tube 5B" and thence to the interior of the. roll itself. The return circulation. is effected through the ports 52 in' the discs 5| and also in. the. annular space surroundingthe tube. 50;, dischargebeing" effected through the annular passage. 55' and ultimately through theflexible hose 5.4.

Similar connections for circulation of heat transfer medium through, roll l2 are provided, the flexible hose connections for this roll being indicated in. Figure '7' at 51 and 58.

By virtue of the employment of the flexible hose, connections, any requiredadjustments in relative positions of the. rolls may be accommodated.

The heattransf-er medium. may be circulated through the rolls for the purpose. of heatin up the rolls prior to feed of molten nylon thereto; and. during strip formation this heat transfer medium is: employed. for close. regulation of the roll temperatura. according to the particular conditions; of. operation. Such close. regulation is advantageously achieved by employment of thermostatic control of heat transfer equipment through which the medium is passed after it is discharged fromthe rolls and beforelitis. returned thereto. For most operations, especially where substantial quantities. or molten material. are beof the forming rolls HI2,and the pressure of interengagement of the drawing rolls with the formed strip, and also the frictional characteristics of the drawing rolls should be such that considerable tension is provided; v

The tension applied by the drawing rolls signi ficantly affects the propertiesof the finished strip. Generally speaking, the fabrication of relatively thin strip, i. e., strip thinner than .020", requires greater tension than the fabrication of relatively thick strip, for example, strip whose thickness exceeds .050". The application of considerable tension during the fabrication of thinstrip is important in producing strip substantially. free of wrinkles, and also is of importance in avoid ing the tendency for the formed strip. to take a set with sharp curvature. 7 f i The eflect' of tension-in overcoming the tendency to waviness' is apparent in the following tables, in which are compared the characteristics of strip of several thicknesses, fabricated in separate runs in which the only variation in operating conditions was the tension applied to the strip. It should be emphasized that because of the'difficulty of accurately measuring. tension the individual figures are subject to some margin of error although the relative results for thevarious gauges are considered entirely representativeof true conditions of operation.

Table 1 These examples illustrate the effect of'varying the tension applied to the strip in the fabrication of material of .0l1 to.012" thick and 2%" to 2 wide. The unit. pressures were compiled on the basis of separate measurement of the cross sectional area for each run.

Characteristics of Lbs. Tension Inch Tape breaks. 900 Normal tension. Somewhat wavy. Very wavy.

Table 2' Characteristics of Lbs/Sq. Lbs. Tension Inch ape 3, 900 Tape breaks. 3, 400 Normal tension. 560 Somewhat wavy.

57 Very wavy.

Table 3 I v These examples illustrate the effect of varying tension on tape .018" to .019" in thickness and to 2 wide. 4

Characteristics of Tape breaks. Normal tension. Somewhat wavy.

Table 4 v Lbs/Sq. Characteristics of Lbs. Tension Inch Tape 21 127 Tape breaks. l6 97 Normal tension.

- breaks.

It will be seen from the data set forth above that when working with thin strip the range for producing tape which is free from waviness is upwards of lbs/sq. in. and preferably upwards of 450 lbs/sq. in., the upper limit of tension being established by the point at which the strip It should be pointed out in connection with the upper limit that in the examples above set forth, the apparatus was operated with the water level in the bath illustrated in Figure 1 somewhat higher than that illustrated in the figure, that is to say, the experimental data was obtained when the bath level was almost touching the lower portion or the rolls for the strip below .020" thickness, and in contact with the rolls on the .060" to-.062. material. We have found that as the water level is lowered it be comes increasinglymore diflicult to break the tape. In particular, we have found that when the level of the bath is'at leasttwo inches below the point where the tape leaves the forming rolls, the .018 tape (the subject matter of Table 3) cannot be broken at all, but rather undergoes elongation, with corresponding orientation of the molecules.

The liquid bath in the vessel 1 serves to bring down the temperature of the formed strip, so that it may readily be handled as it is delivered from the equipment. In some cases the level of the liquid cooling bath may be somewhat higher than indicated in Figurel and may be sufficiently high to contact the lower portions of the rolls,

although for accuracy of temperature regulation of the rolls, it is preferred to avoid contact of the liquid with the rolls.

Water may be employed as the cooling liquid in the bath and it is contemplated to employ some rust preventive or inhibitor therein, especially in the event of contact of the bath with the rolls, a particularly eifective inhibitor being potassium bichromate, which serves the purpose but at the same time is not subject to being carried out of the bath on the formed strip. In the event that the bath level is kept high enough to contact the rolls it is contemplated that the rolls be equipped with wipers to remove water therefrom, for instance wipers of the character disclosed in the copending application of Montross and Schurr,

Serial No, 38,966, filed July 16, 1948, issued as Patent No. 2,624,913 on January 13, 1953, which application is assignedto the assignee oi the present application.

When making thin stri we have found that this tendency for the strip to coil up sharply is also influenced by the position of the guide element 34' and can be greatly diminished when the guide element is positioned substantially below the forming rolls, i. e., so that the initial run of the strip beingdrawn from the forming rolls, extends in a path substantially in alignment with the pass between the rolls. A position such as indicated in full lines in Figure l is desirable when making very thin strip, although the positien; may be shiited somewhat, for instance to. the position indicated in dotted lines at 34c, de-. pent-ling upon the thickness of the strip being iormed.

Still another important factor in producing thin strip of good quality and especially thin strip having a minimum of transverse ridges or wrinkles is the temperature of the forming rolls. According to, the invention, when making relatively thin strip, for instance less than .015" in thickness, the temperature of the forming rolls should be quite accurately controlled within temperature ranges as given herebelow.

To consider an example of preferred temperature conditions, reference is made to .a typical operation, producing strip from polyhexamethylene adipamide, which has a melting point of about 507 F; and a somewhat lower freezing point at about 473 F; When forming strip from this polyamide, it is preferred to deliver the molten polyamide to the: entrance nip of the forming rolls at a temperature somewhat above the freezing point, but preferably not substantially above the melting temperature,- an efiece tive range being from 480 F. to. 515? F. Somewhat higher temperatures may be used, for instance up to about 550 but excessively high temperatures are to be avoided because of the tendency for the material to form bubbles and to oxidize. Moreover, excessively high tempera:- tures' interfere with the desired solidification of the material as it passes through the rolls. M

It should be borne in mind that the temperature of the rolls is dependent not only on the temperature of the roll control liquid but also on the volume and temperature of the molten nylon being fed to the entrance nip of therolls; In any case, the conditions should be adjusted, so as to maintain a roll temperature above about 180 F. but below about 350 F. when making thin strip from polyhexamethylene adipamide. The temperature is most desirably keptabove 200 F., a particularly effective range. being between 220 F. and 300 F.

In regulating the feed of the molten material, the screw extruder 3| and the speed of the rolls H and I2 should be operated at such rate as to maintain a slight excess or reservoir of the master 8, molten nylon in the entrance nip of the forming rolls. '1

With respect to the reference herein to formation ofstri'p stock, it should be understood that the invention is not only applicable to the production of plain flat. strip but also to strip of shaped section, for instance beaded material or the like, in which event the forming rolls would be appropriately shaped to give the desired strip se t o practicing the invention it is of importance that th pqlramid use be of very l w moisture content prior to melting, preferably below 25% water content by weight. Therefore, we prefer to preliminarily and careiully dry the granular or flake material before melting, and this is especially important in the case of polyhexamethylene adiparni hi h. is r bl c r fully vacuum dried. In the absence of such dryins an exc s b l io m n the mater and the formed strip has lower elongation and ha a endency to br t e s Strip formed in accordance with the present invention is substantially free of bubbles and other detects either within the piece or on the suriacethereof, The edges of the strip are fre-, quently somewhat irregular in view of which trimming is contemplated. The formed strip it: self has excellent physical characteristics, includns t u hn s and hi htensile n th.

In the case. 0i a strip of .010 in thickness, made i 011 a a m ratur r a u 22 F., the tensile strength was 9540 lbs/sq. in., and the elongation 194% in a 2 in. gauge length. 7 The techniques covered by this invention are applicable to polyhexamethylene adipamide with or without fillers such as graphite, coloring ins di s, ntiox ant or h r addi We claim:

The method for forming substantially waveiree strip stock of thickness less than .020" from polyhexamethylene adipamide, which method comprises feeding molten polyamide to :the entrance nip of a pair of forming rolls maintained at a temperature or from 180 to. 35,0 and drawing the formed strip from the forming rolls under a tension of more than lbs/sq. in, but less. than that which would break the strip or appreciably orient the polyamide.

LOUIS L. STOTT. PAUL L. SHURR.

References Cited in the file of this patent UNITED STATE PATENTS Number Name Date 2,048,686 Qonklin July 28, 1936 2,212,712 Graves Aug- 27, 1940 2,244,208. Miles June 3,, 19.41 2,289,774 Graves July 14, 1942 2,295,942 Fields Sept. 15, 1942 

